In thin film metal alloy media for vertical magnetic recording, the magnetic film is typically a single layer of a magnetic alloy having an ordered crystalline structure with its easy axis of magnetization oriented generally perpendicular to the substrate. One type of material used as the magnetic film is a cobalt-chromium (CoCr) alloy which is sputter-deposited on the substrate, or on an intermediate nucleating layer deposited on the substrate, to form a film having a hexagonal close packed (hcp) crystalline structure with the [00.2] axis (the C-axis) oriented generally perpendicular to the substrate. The magnetic properties of thin film metal alloy vertical recording media made with various substrates, a titanium (Ti) nucleating layer and a single-layer CoCr perpendicular magnetic film are described by Kobayashi, et al. in "High Density Perpendicular Magnetic Recording On Rigid Disks", Fujitsu Scientific & Technical Journal, Vol. 19, No. 1 (March 1983), pp. 99-126. The magnetic properties of vertical recording media with an 8000 Angstrom cobalt-chromium-tantalum (CoCrTa) magnetic film deposited on a 1000 Angstrom Cr nucleating layer are described by Langland and Albert in "Recording on Perpendicular Anisotropy Media with Ring Heads", IEEE Transactions on Magnetics, Vol. MAG-17, No. 6 (November 1981), pp. 2547-2549.
In order to achieve a sufficiently high perpendicular coercivity with a single-layer CoCr or CoCrTa alloy magnetic film, it is necessary that a relatively high temperature be applied to the substrate during the sputter deposition process. This limits the formation of CoCr or CoCrTa alloy films to particular types of substrates, such as an aluminum-magnesium (AlMg) alloy or silicon. In addition to high perpendicular coercivity, another desired property of vertical magnetic recording media is a high ratio of perpendicular to horizontal coercivity. When a single layer CoCr alloy film is used as the magnetic layer, the in-plane or horizontal coercivity is relatively high, which limits the achievable value of this ratio. Even though both the perpendicular and horizontal coercivities of a CoCr film are known to increase with an increase in substrate temperature during film deposition, the ratio of perpendicular to horizontal coercivity remains relatively constant regardless of the temperature of the substrate during deposition.